Glycol esters of alkyl-mercapto-carboxylic acids



Patented June 17, 1952 GLYCOL ESTERS OF ALKYL-MERCAPTO- CARBOXYLIC ACIDS Paul 'V. smith, Jr., and Louis A. Mikeska, Westfield, N. J and Alexander H. Popkin, New York, N. Y., assignors to Standard Oil Development Company, a. corporation of Delaware N o Drawing. Application September 24, 1948,

Serial No. 51,112

I 6 Claims.

1 This invention-relates to a new class of compounds which have been found to be particularly suitable for use as synthetic lubricants because of their low pour points, high viscosity indices and good load-carrying characteristics. 7

In the lubricant art, considerable progress has. been realized in recent years in the production of lubricants characterized by one or more specific properties and adapted for particular uses. In the main, this progress can be attributed to two developments: the first, new refining procedures, and the second, addition agents capable of imparting particular properties to available lubricants. Thus, viscosity index improvers and pour depressants are added to automotive lubricants to render the lubricants more adaptable to wide changes in temperature conditions, while other agents are added to improve the load-carrying properties of a lubricant which is to be employed, for example, under extreme pressure conditions.

Recently, in an effort to obtain superior lubricants endowed with specific and superior characteristics, a new field has been explored, namely, the synthesis of lubricants from various materials. Esters represent one class of materials which have attracted unusual interest as synthetic lubricants. In general, they are characterized by higher viscosity indices and lower pour points than mineral oils of corresponding viscosity. The esters described in the present speciflcation have been found to exhibit very low pour points, high viscosity indices, and in addition unusually good load-carrying properties. Lubricantspossessing such properties are of special.

value in the lubrication of engines which are sub- Jected to high temperatures such as combustion turbine engines, particularly those of the "propjet type. Mineral oil lubricants containing added viscosity index improvers, thickeners or other highly non-volatile additives are undesirable for use insuch engines because of the tendency to leave a residue which would accumulate and interfere with the operation of the engine. A synthetic lubricant of the type described in the present specification is especially adapted to use under such conditions, since the lubricant contains no additives and thus tends to leave no residue upon volatilization.

The new compounds of the present invention which have been found to be useful as synthetic lubricating oils are glycol esters of sulfur-containing monocarboxylic acids. The glycols may be the paraffin glycols or they may be glycols containingoxygen'or sulfur ingether or thioether linkages. I r

where R and R. are open chain aliphatic hydrocarbon radicals containing 2 to 22 carbon atoms, 0

one or both of which contains a sulfur atom, and may be saturated or unsaturated and may consist of straight orbranched chains. The sulfur atom is present as a thioether linkage and is separated from the carboxyl group by at least one carbon atom. The radicals R and R. may be alike or different. R." of the formula may be a saturated aliphatic hydrocarbon group, straight chain or branched, containing 2 to 18 carbon atoms, or

it may be a series of saturated aliphatic hydrocarbon radicals linked by oxygen or sulfur atoms, or by both oxygen and sulfur atoms, provided there are at least two carbon atoms between each carboxyl group and the nearest oxygen or sulfur atom and at least two carbon atoms between each oxygen or sulfur atom in the chain, and provided further that the total number of carbon and oxygen or sulfur atoms in the entire R" radical is from 5 to and that there are not more than two sulfur atoms in'the chain. The compound should have a molecular weight of at least 300.

Many of the sulfur-containing acids employed in preparing the esters of the present invention may be conveniently prepared by reacting an olefin, e. g., diisobutylene, with hydrogen sulfide to form an alkyl mercaptan, after which the mercaptan is reacted with acrylonitrile to form the fl-alkylmercaptopropionitrile, and the latter is in turn hydrolyzed to form the fl-alkylmercaptopropionic acid. In general, mercaptans react very readily with acrylonitrile or acrylic acid esters to give acids containing sulfur atoms. The mercaptans may be formed from readily obtainable olefins and olefin polymers such as propylene, isobutylene, diisobutylene, triisobutylene, propylene polymers, and the like. Sulfur-containing acids may also be prepared by the reaction of halo-acids with mercaptans, by the addition of mercaptans to unsaturated acids, or by the addi tion of thioglycolic acid to olefins. It is not intended that this invention be limited to the 3- alkylmercaptopropionic acids, although they are preferred from the standpoint of ease of preparation and cost. Acids suitable for use in accordance with the present invention are typified by compounds such as ethylmercaptoacetic acid, 8.- methylmercaptopropionic acid, e-ethylmercapto- 3 propionic acid, ,a sec. butylmercaptopropionic acid, ,B-tert.-butylmercaptopropionic acid, c-tertoctylmercaptopropionic acid, ,8 tert. dodecylmercaptopropionic acid, ,6 cetylmercaptopropicnic acid, s-allylmercaptopropionic acid, 'yoctylmercaptobutyric acid, Y-dodecylmercaptobutyric acid, -hexadecylmercaptobutyric acid, w-octylmercaptoundecanoic acid, w-dodecylmercaptoundecanoic acid, w-hexadecylmercaptoun- 4 dodecylmercaptopropionic acid with various glycols. The last two of the above-named acids were prepared as follows: To a mixture of 12 cc. of Triton B (benzyltrimethylammonium hydroxide). a,nd 2,mols,of themercaptanlprepared by reacting diisobutylene or;;t riisobutylcne with hydrogen sulfide) was added dropwise 3 mols of :acrylonitrile at such a rate as to keep the temperature below 50 C. The mixture was then decanoic acid, cyclopentenylmercaptoacetic=acid,, o rheated to .-50:';C.--'60 C. for two hours, after pentenylmercaptoacetic acid, a-octylmercaptodi- :which the product was poured into water, and methylacetic acid, adodecylmercaptodimethyl an q 1-v.o1um .of. her added and a small acetic acid, a-hexadecylmercaptodimethylacetic quantity ofjhydrochloric acid to neutralize the acid, and the like. .'I r 1t0n-,B.. .1After:stirring, the ether layer was iso- The glycols employed in preparingwtheiestersiiiiailed:washeduwithiwater. dried over sodium sulof the present invention include.ethyleneglYcol fate, and the 11. 1 removed O e Steam bath. and any of the paraflinic homologues of thesame '"rhere m e'was mixed with 2.1 mols of sodium containing up to 18 carbon atoms. These may "hydroxide dissolved in 600 cc. of a 50% aqueous implucle for example ethylene glycol, propylene I ethylzalcohol. This was heated on a steam bath glycol butylene 1 ,;p trimethylene 20 for 40 hours, acidified rwith hydrochloric acid, glycol, tetramethylene glycol, pentamethylene extracted with ether, washed .with ,water, dried glycol, ;and .decamethylene glycol. -:Since ;.-.the ver -Ia desiccant, anddistilledat about,5..mm. glycols may also containoxygen or sulfur atoms, res r compounds such as diethylene glycol, triethylene T -l e t y mercaptopropionicacid,;preglycol, tetraethyleneglycol and the higher memp d by .the,=above. method. .was reacteiwith bers of this series containing carbon and oxygen hyle g ycol. hexamethylene glycol, atoms toacombined total of 80 .(exclusive of hymethylene o te r e hylene glycol, ,and droxyl groups) maybe employed. .The,-,po lyethi di ccl, a e pe fl e yr and [the ,fi-lt rflredoylene glycols-of;the formula ig yh captotimfionic acid also ,prepared, by

I ea oveme o, wasreac ed. with :trimethyltprocedure wherenis 1 ,to'26, anjdithe polyprop'ylene glycois asa generalestcrification procedure: ,'Iwq;mqls of .the general 'formula ofthe acid and. one mol ofthe glycolaw r mix d :RER: TRIYRE with by :weight .of ;.p-toluenesulfonic.,acid 1 33 mon'ohydrateand about 15,0 ,.cc.,0f benzenepr HOWHCBOWMHOH naphtha. as an entraining fluid. The mixture wherceither'Ri or R2. is a methyl groupandflthe was refluxed jmanappamtus providedfiwithiia other is .hydrogen'and where n is 1 to120 are wateptr p, tilno ,rnore water distilled lover, especially useful. Glycols containing suliur after .whichit .was sodiumvvraiu atoms in thioether linka s may also be em- 49 bonate. solution and .With'Water andQthen dried ployed, andLthese include suclrcompounds as overa ,desiccantsuchlas v Drierite anhydrous thiodiglycol and, 1,2,-bis'(2 -hydroxyethylmercalcium ulfatel. The material was/stripped apt There y also be ed e y ls at. 5..mm.,.t0xa.bath.temperatureqof 200- 220=o. containing 'both' oxygen and sulfur in similar The esters prepared by the aboye. mtfibd linkages. Such .a compound ,is ,bis-,-"[2'-1.(2-hyi5 testedwith respect t variousjpmbe'rfies h c fl o yo y) ethyl] Su fi .are of interestinconnection.with-theirip p ig "The esterificationprocess-maybe carried-zout use .asisyntheticlubricating oils, thereSuItsbm by known ester'ification means, preferably with shown,.below.inlthe table of data. 0

- l Machine Kinematic UVtsc oslty 7 ASTM Acid v "Glycol *fi Ptar 1 5 pc kln-aex 100%. 210 F I oil -ltthyimercapto-aeeticfl JPolyprgmyleneglycol 43.070 7:805 0.634 142 15 7 flflgfigybmercarto- Tnmctnyleneglycol" 4311590 1-503 @1725 vV110 Hi6 I u i y A A intrastate.- tit it? is; a Do ict raethylene glycol 50.745 7.764 0.080 '12; ..'35 15 Do Tn lq.dlglyco l--- use 15.852 -,o;ess n6 -5 15 7 fi XBl't-DPd-QCYlrIHPI(18p- .Trimethylene glycol... 163.6 12.20? {L764 60 8 =-top ropxomc. I

-HYIBfinEd'Goastal-naphthenlc ciloMOseconds Sa bolt vi o it i 0 .s, 7 A ciicnrrisnot'mcrethantw 'wei ht enthemmen achine." y y at 2 o gable-med milieu] 9 Molecular weight 400. the -;ll$8;i0f ;-a catalyst such as p-toluenesulion-ic acid. all; an ester. contalni -ngtwo: 'difierent acid radi'calais desired, the glycol is reacted :with a mixture ;nf;-acids.

sgrllataswill be-givenabelow-showing-the properties ofsseven'texamples f -;esters which illustrate .the present -tinvention,ithese estersmhaving -been preparedbyzesterifyi-ng.ethylmercaptoacetic acid, -5- tertt-aoctylmercal mpropionic f acid and la-tort.-

The, abovedatas indicate; that ;the.,es,ters possess characteristics which;.;ren,d.er them'ssuitablei-for general :use as .-lubricati1 ig v oils. IThB'fQStGIS oi th e -present invention may also-be blended; with m neral lubricating oils -to ;give lubricantsyof iinproved viscosity index, pour point, .and 'loadcarrymg Q-apacity. 'Fonth purpose ofincreasine. thefllmstr st and load-carrying capacity of mineralzciislth esters "are preferably blended in proportions ranging from 1 to by weight of the mineral oil. The data in the last column of the table of data show the usefulness of these compounds when blended with a mineral oil. The unblended mineral oil employed in these tests was capable of carrying only one or two weights on the Almen machine under similar conditions of test.

The mineral lubricating oil base stocks which may be improved in load-carrying capacity by the addition of the new compounds of the present invention may be derived from various types of crude petroleum or may consist of distillates or blends of various kinds which have been refined by any of the conventional methods. Synthetic oils may also be used such as those obtained by the polymerization of olefins or the hydrogenation of coal or its products. The base oils may vary considerably in viscosity and other properties depending upon the particular uses for which they are desired.

If desired, other known addition agents, such as thickeners, pour depressants, antioxidants, dyes, etc., may be added to the mineral oil composition prepared in accordance with this invention.

What is claimed is:

1. As a new composition of matter a compound of the formula n'coo where R and R, are open chain aliphatic hydrocarbon radicals containing 2 to 22 carbon atoms, at least one of the radicals containing a sulfur atom as a thioether linkage, the sulfur atom being separated from the CO0 group by at least one carbon atom, and where R" is an organic radical selected from the group consisting of (1) saturated aliphatic hydrocarbon radicals of 2 to 18 carbon atoms and (2) radicals consisting of series of saturated aliphatic hydrocarbon radicals linked through at least one non-carbon atom of the group consisting of oxygen and sulfur, not more than two sulfur atoms being in the radical, each hydrocarbon radical so linked by a non-carbon atom containing at least two carbon atoms, the sum of the carbon atoms and said non-carbon atoms in the entire radical being from 5 to 80, and the molecular weight of the entire compound being at least 300.

2. A composition according to claim 1 in which R and R are fl-tertiary-octylmercaptoethyl groups and R" is a saturated hydrocarbon group.

3. A composition according to claim 1 in which R and R are [3-tertiary-octylmercaptoethyl groups and R" is a polyethylene glycol radical.

4, As a new composition of matter the hexamethylene glycol ester of S-tert-octylmercaptopropionic acid.

5. As a new composition of matter the triethylene glycol ester of ,B-tert.-octylmercaptopropionic acid.

6. As a new composition of matter the tetraethylene glycol ester of c-tert-octylmercaptopropionic acid.

PAUL V. SMITH, JR. LOUIS A. MIKESKA. ALEXANDER H. POPKIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,534,752 Watson Apr. 21, 1925 1,807,304 Calvert May 26, 1931 2,164,393 Evans July 4, 1939 2,262,686 Kyrides Nov. 11, 1941 2,268,185 Burke Dec. 30, 1941 2,422,246 Lazier June 17, 1947 

1. AS A NEW COMPOSITION OF MATTER A COMPOUND OF THE FORMULA 